Pathways to Self-Assembly of Ultra-Narrow Size Distributions of Heteroepitaxial Semiconductor Quantum Dots

本项目研究的是异质外延半导体相干岛量子点的自组装。方法是研究Ge/Si（100）体系中自组装的原子机制；因为，尽管Ge/Si（100）是观察到的最简单的自组装系统，但它保留了许多在更复杂的合金半导体系统（如SiGe/Si， InGaAs/GaAs）中观察到的自组装相关行为。各种原位和非原位显微镜（扫描隧道、原子力、扫描和透射电子显微镜）将被用来表征利用分子束外延（MBE）和化学气相沉积（CVD）形成的自组装量子点（SAQD）的集成。实验可及参数的相空间；为了确定在SAQD整体中获得所需尺寸和形状均匀性的途径，将系统地研究衬底温度、沉积速率、总覆盖率和生长后退火。一个主要目标是获得这种均匀性，同时保持灵活性，以改变点尺寸分布的平均半径和点的面密度从样本到样本。利用光致发光光谱法将观察到的Ge/Si(100) SAQD的形貌与其光学性质相关联。实验研究将通过进一步发展应变岛屿系统的微观结构演变模型加以补充。该模型结合了相干岛的弹性能和远离应变岛的扩散偏差，该偏差随岛的大小而增加。进一步深入了解自组装过程将获得通过动力学蒙特卡罗模拟应变岛生长。该项目涉及具有高技术相关性的材料科学主题领域的基础研究问题。该研究将在基础层面上为电子/光子器件的重要方面贡献基础材料科学知识。现在有了实验工具，可以在原子水平上观察基本过程，一旦对这些过程有了更好的了解，就会促进基础科学和技术的进步。从研究中获得的基本知识和理解预计将有助于提高先进器件和电路的性能和稳定性，为设计和生产改进的材料和材料组合提供基本的理解和基础。该计划的一个重要特点是通过培养学生在一个基础和技术上重要的领域的研究和教育的整合。＊＊＊

9804310 Drucker This project addresses self-assembly of heteroepitaxial semiconductor coherent island quantum dots. The approach is to study atomistic mechanisms of self-assembly in the Ge/Si(100) system; since, although Ge/Si(100) is the simplest system for which self-assembly has been observed, it retains much of the self-assembly related behavior observed in more complex alloy semiconductor systems such as SiGe/Si, InGaAs/GaAs. A variety of in and ex situ microscopies (scanning tunneling, atomic force and scanning and transmission electron microscopies) will be employed to characterize ensembles of self-assembled quantum dots (SAQD) formed using molecular beam epitaxy (MBE) and chemical vapor deposition (CVD). The phase-space of experimentally accessible parameters; substrate temperature, deposition rate, total coverage and postgrowth annealing, will be systematically investigated in order to identify pathways to obtaining desired size and shape uniformity throughout the ensemble of SAQD. A primary goal is to obtain this uniformity while retaining the flexibility for varying the mean radius of the dot size distribution and the areal density of the dots from sample to sample. The observed morphology of the Ge/Si(100) SAQD will be correlated with their optical properties using photoluminescence spectroscopy. The experimental investigations will be complemented by further development of a model of microstructural evolution in strained island systems. This model incorporates the elastic energy of coherent islands and a diffusion bias away from strained islands which increases with island size. Further insight into the self-assembly process will be gained through kinetic Monte Carlo simulations of strained island growth. %%% The project addresses basic research issues in a topical area of materials science having high technological relevance. The research will contribute basic materials science knowledge at a fundamental level to important aspects of electroni c/photonic devices. Experimental tools are now available to allow atomic level observation of elementary processes which when better understood will allow advances in both fundamental science and technology. The basic knowledge and understanding gained from the research is expected to contribute to improving the performance and stability of advanced devices and circuits by providing a fundamental understanding and a basis for designing and producing improved materials, and materials combinations. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area. ***